Flame ignition

ABSTRACT

Burner ignition employing flame rectification to produce signal pulses to retain fuel supply valve open, and employing pulses from closing AC power circuit for initiating opening of the valve. The full specification should be consulted for an understanding of the invention.

United States Patent 1191 [ill Potts 14 1 Apr. 10, 1973' [54] F LANIE IGNITION [56] References Cited [75] Inventor: William F. POflS, LIVCIPOOI, N.Y. UNITED [73] Assignee: Liberty C(lrlmafion, 3,447,880 6/1969 Potts et a1 ..43 1/66 Syracuse, NY 3,358,474 12/1967 Liesse ..431/255 22 Pl d: l 15, 1970 1 1 8 Ju Primary ExaminerEdward G. Favors [21] Appl. No.1 55,234 Attorney-F. P. Keiper Related us. Application Data [57] ABSTRACT I [62] Division of Ser. No. 732,459, May 27, 1968, aban- Burner ignition employing flame rectification to Cloned produce signal pulses to retain fuel supply valve open, and employing pulses from closing AC power circuit [52] US. Cl ..431/78, 431/254 for initiating Opening of the valve The fun specifica on Shculd be u ed for n nd sta di g o h ['58] Field of Search ..43 1/66, 78, 80, 254, invention I 431/255 1 Claim, 6 Drawing Figures PATENTEB APR 1 0 I975 snmlnf FIG. 2

FICLI INVENTOR. WILLIAM F. POTTS,

k wk

ATTORNEY PATENTED (H573 $726,530

SHEET an? 3 I INVENTOR. WILLIAM EPOTTS.

ATTORNEY FLAME IGNITION This application is a division of application 732,459 filed May 27, l968 and now abandoned.

This invention relates to an improvement in fluid fuel burner systems, and more particularly relates to burner ignition and control of burning with safety shut-down after a trial for ignition, employing a high voltage spark at the burner to ignite the fuel and flame rectification phenomena for proving the presence or absence of flame at the burner.

In the heating industry, standards have been established which require that the main burner flame be monitored directly, particularly in the case of large input burners, while in other cases it has been the practice to ignite the main burner by use of a pilot burner and proving only that the pilot burner is ignited. In still further cases it has been the practice to ignite the pilot, prove that the pilot is burning, open the main burner valve and then prove that the main burner has ignited, all of this being incorporated with appropriate trial for ignition and safety shut-down means. Furthermore, in many types of burner applications coming into more wide scale use today, the presence of a constant burning pilot can be deleterious to the equipment, particularly during non-heating periods of the year. Thus, it is in the interests of the heating industry to simplify the ignition and control means for any burner both for the purpose of reducing cost and increasing reliability and life expectancy.

The present invention is directed to providing low cost highly reliable spark ignition of the main burner directly without recourse to a pilot burner, while maintaining the high standards of safety required in a fluid fuel burner control by employing flame rectification phenomena for detecting flame.

Accordingly, it is an object of the invention to provide ignition means adequate to ignite a gas burner by electric spark discharges.

Another object of the invention is to provide optional means to allow sparks to occur during the burning period of the burner or to allow sparks to occur only in the absence of flame at the burner and to discontinue the occurrence when the flame is present.

A further object of the invention is to employ flame rectification means to control a safety shut-down timer means.

A still further object of the invention is to provide a fail-safe safety timer and lock-out means wherein any component failure will result in the closing of the gas valve to the burner.

Yet another object of the invention is to provide such an ignition and control system having inherently long life and high reliability.

The above objects and other features of the invention will appear more fully hereinafter from the following detailed description when taken in conjunction with the accompanying drawings. It is expressly understood that the drawings are employed for purposes of illustration only and are not designed as a definition of the limits of the invention, reference being had for this purpose to the appended claims.

Referring to the drawings wherein like reference characters indicate like parts:

FIG. 1 is a schematic diagram of a subcombination of the invention;

FIG. 2 is a schematic diagram of a variation of the subcombination of FIG. 1;

FIG. 3 is a schematic diagram of one embodiment of the invention;

FIG. 4 is a schematic diagram of another embodiment of the invention;

FIG. 5 is a schematic diagram of a further embodiment of the invention; and

FIG. 6 is a schematic diagram of a still further embodiment of the invention.

With reference to FIG. 1, there is shown a flame sensitive circuit employing flame rectification to obtain a signal output across resistor 24 to positively indicate the presence of flame. With an alternating current source of power, nominally volts, applied to terminals 20 and 22, the latter being connected to ground, when electrode 28 which is spaced from the grounded burner 30 is immersed in flame from the burner, the applied voltage will cause current to flow through resistor 24, resistor 32, electrode 28 through the flame to burner 30 thereby providing a charging path for capacitor 34. Although the applied voltage is alternating, capacitor 34 will tend to charge alternately first in one direction and then in the other, except that since electrode 28 of small area is positioned in an area of high ionization of the flame from burner 30 which is relatively large in area, the flame from burner 30 under these circumstances takes on the characteristics of a rectifying diode, that is, a medium which has better conductivity in one direction than in the opposite direction. Thus, when terminal 20 is going positive relative to ground, capacitor 34 will charge with the polarity shown, that is, with the plate connected to resistor 24 being positive, and on the alternate half cycle when terminal 22 is positive with respect to terminal 20 the capacitor will discharge but not fully, thus leaving a net V positive charge as indicated in FIG. 1. This net charge builds up rapidly to the point where it will cause voltage breakdown device 36 to conduct, discharging capacitor 34 through resistor 24, thus periodically producing pulses of voltage as an output signal.

When electrode 28 is not enveloped in flame from burner 30 there is no charging path for capacitor 34 and consequently there is no output signal. Since the voltage applied from the source of power is considerably in excess'of the breakdown device 36, it is necessary to include resistor 32 so that in the event of an inadvertent ground of electrode 28 to burner 30, the breakdown device 36 will not be damaged. However, in order to maintain the integrity of the circuit as a flame rectification system it is necessary to make the time constant of resistor 32 and capacitor 34 sufficiently long so that the device 36 will not be triggered if electrode 28 is grounded to burner 30. The time constant of resistor 32 and capacitor 34 will be determined by the frequency of the applied alternating voltage. Thus, a

useful, dependable signal is obtained when flame from burner 30 envelops electrode 28 and which signal is absent when there is no flame or when electrode 28 is grounded.

In FIG. 2 there is shown an alternate method of employing the flame rectification means whereina pulse transformer 26 is used to electrically isolate the output signal from the line connected to terminal 20.

In FIG. 3 there is shown an ignition and control circuit employing the previously described flame rectification phenomena including a spark voltage generator of the capacitive discharge type, and means for providing an initial trial for ignition period after which lockout or safety shut-down will occur if flame is not proven to be enveloping electrode 28, and further means for preventing the control system from being reenergized for a predetermined period of time after the applied power has first been removed from the circuit. When an alternating current source of power, nominally 120 volts, is applied to terminals20 and 22, the latter being grounded and connected to common ground line 38,

the gate of silicon controlled rectifier 44 will receive trigger pulses when ground line 38 goes positive via normally closed contacts 46 of heater switch 48, the anode and cathode in that order of rectifier diode 50, capacitor 52, these pulses occurring during the charging of capacitor 52 which is fully charged after several cycles and remains charged so long as power is connected to terminals 20 and 22. When SCR-44 is thus triggered into conduction it allows capacitor 56 to charge through resistor 58, the charge reaching a maximum becaUse of the short time constant of resistor 58 and capacitor 56, and at the same time energizing relay 60 through resistor 62. The time constant determined by the sum of the resistances of resistors 62 and 58 plus the winding resistance of relay 60 and capacitor 56, provides a predetermined trial for ignition period after which relay 60 will drop out. In practice, this period is approximately 3 to seconds.

When relay 60 is thus energized it closes its normally open contacts 64 to connect power to solenoid 42 of gas valve 40 through the heater 48 of a safety relay thereby causing valve 40 to open and fuel to issue at burner 30, and at the same time energizes spark generator 66. Spark generator 66 comprises resistor 68, rectifier diode 70, capacitor 72, high voltage transformer 74, silicon controlled rectifier 76, resistor 78, capacitor 80, voltage breakdown device 82 and resistor 84. The secondary winding of transformer 84 is-connected to ground line 38 and to the high voltage terminal 86, said terminal providing means for extending connection from the spark generator 66 to spark electrode 88 located adjacent to the burner 30 whereby the voltage output of transformer 74 will cause spark discharges to occur between electrode 88 and burner 30 thereby igniting fuel issuing from burner 30. When fuel from burner 30 is ignited, flame from the burner will envelope electrode 28 which is connected to resistor 32 via terminal 90, the other side of resistor 32 going through voltage breakdown device 36 and fuse 92 to terminal 20, the junction of resistor 32 and device 36 being connected through capacitor 34 and resistor 94 to the gate of silicon controlled rectifier 44, the gate of rectifier 44 also being connected to fuse 92 through resistor 96. Resistor 96 provides a damping effect to prevent transient voltages from inadvertently triggering rectifier 44 into conduction.

As previously described, when electrode 28 is enveloped in flame from burner 30, pulses of voltage will occur across resistors 94 and 96 from the discharge of capacitor 34 occasioned by the breakdown of device 36, thus triggering SCR 44 into conduction each time a pulse occurs and thus keeping relay 60 energized. After each such pulse a new trial for ignition period begins. The function of resistor 94 is to limit the current to the gate of SCR 44 when capacitor 34 discharges and, as will be hereinafter described, to provide isolation As will be apparent from the foregoing, each time that between the gate of SCR 44 and another SCR to be introduced in another embodiment of the invention. In the event flame from burner 30 fails'to envelop electrode 28 before the end of the trial for ignition period, relay 60 will become deenergized when the charge on capacitor 56 can no longer provide hold-in current for the relay, with the result that contact 64 will open and valve 42 will close and spark generator 66 will cease to function.

The system cannot operate again until the applied voltage is momentarily disconnected and capacitor 52 has discharged through resistor 51 during the disconnect period. Furthermore, if the valve has been energized for more than a few seconds safety relay heater 48 will'cause its normally closed contact 46 to open thereby assuring that SCR 44 cannot be re-triggered after power is disconnected for the period of time that it takes safety heater 48 to cool off sufficiently to close its contact 46. Capacitor 98 connected between the anode and the cathode of SCR 44 is included to prevent transient voltage from inadvertently triggering SCR 44 into conduction. In this embodiment of the invention sparks will continue to occur during the burning cycle of the control so long as relay 60 is energized.

power is initially applied to terminals 20 and 22, the system will not begin to function until SCR 44 has received its initial triggering pulse via contact 46, diode 50, and capacitor 52. Rectifier diode 54 is connected as shown so that in the event diode 54 short circuits, fuse 92 will blow. Furthermore resistor 96 is sufficiently low in value so that if capacitor 52 short circuits fuse 92 will blow.

In FIG. 4, there is shown a system similar to that previously described under FIG. 3 but differing in two respects. First, when power is first applied to terminals 20 and 22 and when terminal 22 first goes positive with respect to terminal 20, normally closed, contacts 100 of alternating current actuated relay 102 will allow a current to flow from line 38 through contact 100, resistor 54 and the gate and cathode of SCR 44 thereby providing an initial triggering pulse to SCR 44 to charge capacitor 56. Although capacitor 56 is charged to a maximum during this period, relay 60 cannot energize from the charge on capacitor 56 because normally open contact 104 of relay 102 prevents current flow from capacitor 56 to resistor 62 and relay coil 60. However, rectifier diode 106 allows relay 102 to be energized on this same half-cycle. The time relay 102 takes to open contact 100 and close contacts 104 is sufficient to trigger SCR 44 and charge capacitor 56. Diode 106 is included so that initially relay 102 can be energized only when line 38 is positive with respect to terminal 20. It will be noted in this arrangement that although relay 102 could possibly fail to operate and capacitor 56 could be charged up as a result of the initial and continuing triggering pulses through contact 100 and resistor 54 to SCR 44, relay 60 can not be energized until contacts 104 close.

When relay 102 pulls in and contacts 104 close, relay 60 will be energized for the trial for ignition period, this being assured by the opening of contacts 100 so that for further triggering of SCR 44, flame must occur at burner 32 and envelope electrode 28 as previously described. When relay 60 is energized, contacts 64 close to connect power to valve 40 through safety heater 48 via terminals 39 and 41 to solenoid 42 and to spark generator 55, and the system then will continue to operate as previously described. With the addition of SCR 108, also triggered by the signal from the flame rectification circuit via line 110 and resistor 112 and 114 at a time when line 38 is positive, each time SCR 108 conducts it will discharge triggering capacitor 80 in spark generator 66 through resistor 116 thereby preventing the spark generator from producing sparks as long as there is a signal output from the flame rectification circuit.

In the event of a flame-out at burner 30 whereby electrode 28 is no longer enveloped in flame, SCR 108 will no longer receive triggering pulses and spark generator 66 will immediately begin to produce sparks again and will continue to do so during the trial for ignition period and will stop sparking either when safety shutdown occurs or alternatively when flame is reestablished at the burner and the flame rectification circuit is again producing triggering pulses. As previously described, when safety relay heater 48 heats up sufficiently to open its normally closed contact 46, the system is thereby prevented from operating for a predetermined period of time after initial removal of power from terminals and 22 or after a safety shutdown occurs. It will be apparent from FIG. 4 that should it be desirable to let the spark generator continue to function throughout the burning period of the heating cycle, this may be readily achieved by deleting components 110, 112, 114, 116 and 108 so that the spark generator is unaffected by triggering pulses from the flame rectification circuit.

In FIG. 5, there is shown the same ignition and control circuit as described in FIG. 4, with the exception that an additional timing arrangement has been provided comprising components 118 through 140 whereby when power is initially applied to terminals 20 and 22, SCR 44 receives a series of triggering pulses through normally closed contact 137 of DC operated relay 136 and resistor 54 thereby causing capacitor 56 to charge from line 38 through resistor 58. However, relay 60 cannot be energized because normally open contact 139 of relay 136 prevents it from doing so. Components 118, 120, 121, 122, 124, 126 and 128, comprise a unijunction transistor timer circuit which provides a triggering pulse to the gate and cathode of SCR 130 after a predetermined period following application of power to the circuit and capacitor 132 will charge from line 38 through normally closed contact 46 of safety heater 48, SCR 130 and resistor 134, and relay 136 is energized. When relay 136 operates, normally open contact 139 closes thereby allowing relay 60 to be energized from the charge on capacitor 56 and setting into motion the normal sequence of events as previously described and normally closed contacts 137 open to prevent any further pulses reaching the gate of SCR 44 from line 38. When contacts 139 close, capacitor 132 continues to be charged, each half-cycle when line 38 is positive, through contacts 139, rectifier diode 140 and resistor 134, thereby keeping relay 136 energized so long as power is applied to terminals 20 and 22. When contacts 46 are open and the power source is momentarily interrupted, relays 136 and 60 will deenergize thereby shutting down the system but since the unijunction transistor timer circuit cannot function again until safety heater 48 has cooled down sufficiently to close contacts 46. Consequently on a momentary power line failure, both the cooling period of safety heater 48 and the timing period of the unijunction transistor timer must elapse before the system will function to re-light the burner.

As will be readily apparent to anyone skilled in the art, should it be necessary or desirable to operate any of the three embodiments of the invention outlined in FIGS. 3, 4 or 5 above, from a 24 volt alternating current power source rather than a l20 volt power source, this can be readily arranged by using a step-up transformer to raise the 24 volt supply to volts, the secondary of the transformer being connected to terminals 20 and 22 in any of these arrangements. However, where a 24 volt control voltage is available, solenoid 42 of valve 40 normally is a 24 volt actuated solenoid rather than 120 volt and, as will be apparent, an additional set of normally open contacts will be required on relay 60 so that terminals 39 and 41 may be provided with 24 volts through safety heater 48 and the additional contacts, thus bypassing the 120 volt portion 'of the circuit. The additional contacts are not shown in the diagram.

In FIG. 6 there is shown an ignition and control circuit which provides spark ignition for up to five burners and which controls one or more of these burners by the flame rectification method. Five spark discharge gaps are formed by electrode pairs 144, 146, 148, and 152, and are series connected so they may be simultaneously energized from a single spark generator source and furthermore are disposed respectively at burners 154, 156, 158, and 162 to ignite fuel by spark discharges in their respective gaps issuing from their respective burners. Fuel may issue from burners 154, 156 and 158 when their respective valve actuating solenoids 166, and 174 open their respective valves 168, 172, and 176. Fuel may issue from burners 160 and 162 when their respective manually operated valves 177 and 179 are opened by their respective control knobs 178 and 180. The output voltage of spark generator 182, comprising a capacitive discharge type spark voltage circuit of components 184, 186, 188, 196, 198, 200, 202 including high voltage transformer 190, is connected from the secondary winding of transformer via terminals 192 and 194 across the series connected electrode pairs 144,146, 148, 150 and 152, whereby on the occurrence of high voltage at terminals 192 and 194 sparks will occur simultaneously at all gaps of said electrode pairs. Alternating current power, nominally 120 volts, is applied to generator 182 via common ground line 204 connected to grounded terminal 206 and ungrounded terminal 208. However,

generator 182 will not function to produce high voltage pulses until its pulsing, or triggering capacitor 198 is charged sufficiently to cause voltage breakdown device 200 to conduct, thus partially discharging capacitor.

by turning knob 178 or 180 respectively. Switches operated by knobs 178 and 180, but not shown, are momentarily closed respectively by knobs 178 and 180 when the respective burner is first turned on whereby the momentary closing of either switch will momentarily apply alternating current power between terminals 206 and 222, thereby allowing capacitor 214 in circuit 210 to charge through rectifier diode 212. Since capacitor 214 is charged momentarily it begins to discharge through resistor 216 and through resistor 218 and diode 220 to charge capacitor 198 in spark generator 182. Capacitor 214 is chosen to have a value considerably greater than that of capacitor 198 so that capacitor 198 may act to cause sparks to occur several times a second for a predetermined period before the charge on capacitor 214 decreases to a value less than the breakdown voltage of device 200 in generator 182. In this fashion, when burner 160 or 162 is first turned on, sparks will occur for a period of time to ignite the fuel issuing from the burner.

When burner 154 is to be operated, alternating current power is applied, by appropriate switching and may include on-off switching by suitable thermostatically responsive means, between terminal 206 and terminal 230 of circuit 224. With power thus applied to circuit 224, two events occur: first, capacitor 198 in generator 182 begins to charge from terminal 230 via fuse 232, resistor 254, diode 256 and common charging line 267, thus initiating sparking; and second capacitor 234 in circuit 224 begins to charge from common ground line 204 through to terminal 230 via diode 236 and the seriesfparallel arrangement of resistors 238, 240, 244 and the gate of silicon controlled rectifier 242, and fuse 232 whereby the portion of this charging current that flows in the gate of SCR 242 will cause SCR 242 to conduct, this action occurring on each half cycle when line 204 is positive with respect to terminal 230 until capacitor 234 is fully charged. Capacitor 234 will then remain fully charged so long as power is applied to terminals 206 and 230. Each time that SCR 242 conducts, it charges capacitor 246 between line 204 through resistor 248, the anode and cathode of SCR 242 and fuse 232 and terminal 230, at the same time energizing solenoid 166 of valve 168 between line 204 and terminal 230 via terminals 253 and 251, resistor 250, the anode and cathode of SCR 242 and fuse 232. Since SCR 242 initially is pulsing on successive negative half-cycles only and, as will be described hereinafter, at much slower intervals, the time constant for the rate of discharge of capacitor 246 as determined by the resistance of solenoid winding 166 plus the value of resistors 248 and 250 is made sufficiently long so that solenoid 166 will haveadequate energization to hold valve 168 open at the slowest expected triggering rate of SCR 242. This time constant may, by appropriate choice of component values and solenoid valve design, be lengthened to several seconds, to provide a predetermined period of'trial for ignition in conjunction with the flame rectification method of detecting flame at the burner.

It will be seen from the above description that when capacitor 234 is fully charged, there will be no further gate current in SCR 242 and valve 168 will close when capacitor 146 has discharged to the point where solenoid 166 is not sufficiently energized to hold the valve open. At this point, if power is removed from terminals 230 and 206, capacitor 234 will discharge slowly through parallel connected resistor 268 so that when power is again applied to the circuit, SCR 242 will be triggered into conduction until capacitor 234 is once more fully charged. In this fashion, a trial for ignition period is provided with closure of the valve at the end of the period.

In this modification, however, electrode 258 is located at burner 154 so as to be enveloped by'flame from the burner, electrode 258 being connected via terminal 259 to flame rectification circuit comprised of capacitor 260 resistors 244, 261 and 262 and voltage breakdown device 264 so that, as previously described, when flame is present at burner 154, SCR 242 will be triggered at regular intervals by the flame rectification circuit, to keep solenoid 166 energized and valve 168 open. In addition, electrode 266, also positioned at burner 154 so as to be enveloped by flame from the burner, is connected via terminal 257 to the junction of resistor 254 and diode 256 whereby the conductivity of the flame in conjunction with resistor 254 will reduce the voltage fed to line 267 via diode 256 to a value less than that required to fire breakdown device 200 in generator 182 so that sparking will cease to be initiated by circuit 224 while electrode 266 is enveloped in flame. In the event of a flame out at the burner 154 whereby electrodes 258 and 266 are no longer enveloped in flame, sparking will immediately be reinitiated by circuit 224 and if the burner fails to reignite before the end of the trial for ignition period the valve will close and remain closed until power is removed from circuit 224 for a few seconds.

In a like manner circuit 226 in conjunction with electrodes 274 and 276 and solenoid 170 and valve 172 control the operation of burner 156, and circuit 228 controls burner 158.

It will be seen that like additional circuits such as 224 may be added for as many additional burners as desired. While the circuit of FIG. 1 produces a positive pulse relative to terminal 20, a negative pulse may be similarly obtained by transposing the breakdown device and capacitance, which results when the terminal is connected between the capacitance 34 and resistance 24, instead of between the breakdown device 36 and resistor 24 as shown.

While several modifications of the invention have been illustrated and'describ'ed, it is to be understood that the invention is not limited thereto. As various changes in the construction and arrangement may be made without departing from the spirit of the invention, as will be apparent to those skilled in the art, reference will be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. For controlling the operation of a plurality of gas fuel burners having respective electrically operable fuel valves which supply fuel to said burners when respectively energized, an ignition and fuel control system comprising in combination: a source of alternating current power one side grounded and connected to said burners, a plurality of spark gaps each positioned relative to a respective burner to ignite fuel issuing therefrom when energized, a plurality of single electrodes each positioned relative to a respective burner so as to be enveloped by flamefrom the burner, a combined ignition and control circuit having connections extending-to said source of power, across said spark gaps, individually to said respective electrodes, and to said respective valves, comprising a capacitive discharge spark generator when operable applying voltage pulses across said spark gaps to energize them simultaneously, a plurality of like control sections each comprising connections extending to a respective burner switch thereby to control the operation of the respective burners, valve energizing means including a silicon controlled rectifier, a relay and a capacitance resistance holding circuit adapted to energize the relay for a predetermined period of time in response to a pulse of voltage on the gate of the silicon controlled rectifier, starting pulse means including a diode, a capacitor and a resistance adapted to provide several pulses of voltage to said silicon controlled rectifier only when power is initially applied to the control circuit and not thereafter until its respective burner switch has been opened, flame responsive means adapted to render operative said spark generator in the absence of flame at the burner and not otherwise, a circuit connecting a respective electrode through a resistor and a gas discharge device to the ungroundedside of said source of alternating current power through said burner switch with a series combination of a capacitor and a resistor across said discharge device adapted to apply pulses of voltage to the gate of said silicon controlled rectifier when said electrode is enveloped'in flame from the burner, and power disconnect means in the line to said burner switch responsive to a significant increase in the average current above the normal current drawn by said control section. 

1. For controlling the operation of a plurality of gas fuel burners having respective electrically operable fuel valves which supply fuel to said burners when respectively energized, an ignition and fuel control system comprising in combination: a source of alternating current power one side grounded and connected to said burners, a plurality of spark gaps each positioned relative to a respective burner to ignite fuel issuing therefrom when energized, a plurality of single electrodes each positioned relative to a respective burner so as to be enveloped by flame from the burner, a combined Ignition and control circuit having connections extending to said source of power, across said spark gaps, individually to said respective electrodes, and to said respective valves, comprising a capacitive discharge spark generator when operable applying voltage pulses across said spark gaps to energize them simultaneously, a plurality of like control sections each comprising connections extending to a respective burner switch thereby to control the operation of the respective burners, valve energizing means including a silicon controlled rectifier, a relay and a capacitance resistance holding circuit adapted to energize the relay for a predetermined period of time in response to a pulse of voltage on the gate of the silicon controlled rectifier, starting pulse means including a diode, a capacitor and a resistance adapted to provide several pulses of voltage to said silicon controlled rectifier only when power is initially applied to the control circuit and not thereafter until its respective burner switch has been opened, flame responsive means adapted to render operative said spark generator in the absence of flame at the burner and not otherwise, a circuit connecting a respective electrode through a resistor and a gas discharge device to the ungrounded side of said source of alternating current power through said burner switch with a series combination of a capacitor and a resistor across said discharge device adapted to apply pulses of voltage to the gate of said silicon controlled rectifier when said electrode is enveloped in flame from the burner, and power disconnect means in the line to said burner switch responsive to a significant increase in the average current above the normal current drawn by said control section. 